Hemicelluloses represent the second most abundant carbohydrate in nature, constituting up to approximately 20-35% of lignocellulosic biomass. Hemicelluloses are heterogeneous polymers of pentoses (e.g., xylose and arabinose), hexoses and sugar acids. It is known that hemicelluloses can be acid-hydrolyzed to xylose and subsequently cyclodehydrated to produce furfural. Over 350,000 tonnes of furfural are produced from xylose annually for applications in plastics, pharmaceuticals and agrochemicals. See for example, Furfural: Hemicelluloses/xylose-derived biochemical, Mamman et al. Biofuels, Bioprod. Bioref. Vol. 2, pp. 438-454.
One of the major challenges for converting biorenewable carbohydrate-derived pentose (e.g., xylose and arabinose derived from hemicellulose) to a broader suite of current commodity and specialty chemicals is the selective removal of oxygen atoms from the carbohydrate. Approaches are known for converting carbon-oxygen single bonds to carbon-hydrogen bonds. See, for example: U.S. Pat. No. 5,516,960; U.S. Patent App. Pub. 2007/0215484 and Japanese Patent No. 78,144,506. Each of these known approaches suffers from various limitations, and we believe that, currently, none of such methods are used industrially for the manufacture of industrial chemicals.
Given the abundance of hemicelluloses, there remains a need for new, industrially scalable methods for the selective and commercially-meaningful conversion of carbon-oxygen single bonds to carbon-hydrogen bonds, especially as applied in connection with the production of chemicals from pentaric acid (and/or derivatives thereof) such as, for example, xylaric acid, and especially for the conversion of pentose (e.g., xylose and arabinose) to valuable chemical intermediates such as glutaric acid, which may be used in the manufacture of diols (e.g., 1,5-pentanediol), diamines (e.g., 1,5-diaminopentane), polyamides, polyesters, polyester polyols, fragrances and pharmaceuticals, among others. See Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH 2009 and also U.S. Pat. Nos. 5,290,852, 5,281,647, 4,439,551, WO 2008/144514 and 2008/070762, Japanese Patents 2005060447 and 2001316311, and U.S. Patent App. Pub. 2008/0103232.